EP0288543B1 - Solar cell system - Google Patents

Solar cell system Download PDF

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Publication number
EP0288543B1
EP0288543B1 EP87907641A EP87907641A EP0288543B1 EP 0288543 B1 EP0288543 B1 EP 0288543B1 EP 87907641 A EP87907641 A EP 87907641A EP 87907641 A EP87907641 A EP 87907641A EP 0288543 B1 EP0288543 B1 EP 0288543B1
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EP
European Patent Office
Prior art keywords
solar cell
solar cells
solar
cells
grid
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EP87907641A
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German (de)
French (fr)
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EP0288543A1 (en
Inventor
M. Edmund Ellion
George Wolff
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Hughes Aircraft Co
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Hughes Aircraft Co
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Priority to US06/929,571 priority patent/US4753683A/en
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier
    • H01L31/068Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0693Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells the devices including, apart from doping material or other impurities, only AIIIBV compounds, e.g. GaAs or InP solar cells
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64GCOSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00Cosmonautic vehicles
    • B64G1/22Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/42Arrangements or adaptations of power supply systems
    • B64G1/44Arrangements or adaptations of power supply systems using radiation, e.g. deployable solar arrays
    • B64G1/443Photovoltaic cell arrays
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042PV modules or arrays of single PV cells
    • H01L31/048Encapsulation of modules
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042PV modules or arrays of single PV cells
    • H01L31/05Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • H01L31/0504Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02SGENERATION OF ELECTRIC POWER BY CONVERSION OF INFRA-RED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30Electrical components
    • H02S40/36Electrical components characterised by special electrical interconnection means between two or more PV modules, e.g. electrical module-to-module connection
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/54Material technologies
    • Y02E10/544Solar cells from Group III-V materials

Abstract

A solar cell array (48) utilizing geometrically alternating, laterally disposed N-on-P and P-on-N gallium arsenide solar cells (26, 70). Improved array efficiency is achieved by placing adjacent solar cells in substantial contact with each other and eliminating bus connections (46) on the top surfaces. This is accomplished by providing the solar cells with a lateral cross-sectional configuration of a parallelogram with the N-on-P solar cells (26) slanted in one lateral direction and the P-on-N solar cells (10) slanted in the opposite direction. The top surfaces of adjacent, contacting solar cells are electrically connected by extending a connector grid (58) across the top surfaces. Strip connectors (60) are used to join the bases of adjacent solar cells.

Description

  • This invention relates to a solar cell module comprising an N-on-P first solar cell including an n-type semiconductor layer and a p-type semiconductor layer, the first N-on-P solar cell having a lateral cross-sectional configuration with a top surface and a first lateral side; a P-on-N second solar cell including a p-type semiconductor layer and an n-type semiconductor layer, the P-on-N second solar cell having a lateral cross-sectional configuration with a top surface and a first lateral side, and connecting means for electrically connecting the n-type layer of the N-on-P first solar cell to the p-type layer of the P-on-N second solar cell, according to the preamble of claim 1. Additionally, it relates to solar cell arrays utilizing such solar cell modules.
  • Semiconductor solar cells are utilized to convert light energy to useable electrical voltages and currents. Briefly, a typical semiconductor solar cell includes an interface between n-type and p-type transparent semiconductor materials. Light shining on the interface creates hole-electron pairs in addition to those otherwise present, and the minority charge carriers migrate across the interface in opposite directions. There is not a compensating flow of majority carriers, so that a net flow of electrical charge results. A useful electrical current is then obtained in an external electrical circuit by forming ohmic contacts to the materials on either side of the interface.
  • Semiconductor solar cells may be produced from a wide variety of semiconductor materials. Silicon solar cells are most widely used, but it has been found that cells fabricated from p-type and n-type gallium arsenide are particularly promising. Such solar cells have higher beginning-of-life efficiency and lower degradation with time and temperature in a space environment, as compared with silicon solar cells. Gallium arsenide solar cells are therefore particularly attractive, and have already found limited use. It is expected that gallium arsenide solar cells will find increased future application, in both space and on earth, particularly if the efficiency of solar cell arrays can be improved and inexpensive fabrication techniques are developed.
  • A gallium arsenide solar cell is fabricated by depositing the appropriate semiconductor layers onto a substrate, and then adding additional components to complete the cell. More specifically, for vapor phase formation, a conventional P-on-N gallium arsenide solar cell is fabricated by epitaxially depositing a layer of n-type gallium arsenide onto a single crystal gallium arsenide substrate, and depositing a layer of p-type gallium arsenide over the layer of n-type gallium arsenide. A P+ layer of gallium aluminium arsenide is deposited over the layer of p-type gallium arsenide to limit surface recombination of charge carriers. A slightly different growth procedure is used when the cells are grown by the liquid phase epitaxial method. A series of thin electrically conductive grids are deposited over the P+ layer in order to carry the electrons from the cell to the collecting bus bar. A transparent cover of glass is applied over the gallium aluminium arsenide to protect the active semiconductor components from physical contact and radiation damage such as encountered in a space environment. The p-type gallium arsenide faces the sun during operation of the cell, as indicated by the terminology "P-on-N" solar cell.
  • The individual solar cells, typically measuring about 2 centimeters by 4 centimeters in lateral dimensions, are joined together in large arrays to produce useable electrical voltages and currents. The arrays may have as many as ten thousand individual solar cells. Since the electrical output of each individual P-on-N solar cell is only about 0.9 volts, in an array a number of P-on-N solar cells are connected in a series fashion to provide an electrical voltage which is the sum of the voltages of the individual series-connected solar cells.
  • To accomplish the series electrical connection, the upper layer (i.e. p-type gallium arsenide) of a first solar cell is connected to the lower layer (i.e. n-type gallium arsenide) of a laterally adjacent second solar cell, and this connection approach is repeated from the second to the third solar cell, and so forth. This connection approach requires that the laterally adjacent solar cells be spaced a sufficient distance apart, typically two millimeters, so that a connector can be inserted between the laterally adjacent cells. A "z" connector is used for making the connection, with the upper leg of the "z" soldered to the top collector bus bar of the first solar cell and the lower leg soldered to the bottom of the laterally adjacent second solar cell. The active area of the cell that is available to produce electricity is reduced by the area covered or shaded by the electrically conductive grids as well as the collector bus bar and the connector attachment to the top surface. The necessary lateral spacing of the cells which permits the insertion of the "z" connector also reduces the electrical efficiency of the array. (The term "efficiency" is used here to mean the electrical output of the array per unit area of the array.) The geometrical limitations thereby imposed on the efficiency of the solar cell arrays, due to the spacing needed between adjacent cells to insert the connectors without producing short circuits between the cells, and the area shaded by the end connections, can significantly reduce the overall efficiency of the array in terms of electrical output per unit area of array.
  • An approach to increase the efficiency of solar cells of the kind described above is disclosed in Patent Abstracts of Japan, Vol. 8, No. 36 (E-227)(1473), February 16, 1984, & JP-A-58194378 (KOMATSU DENSHI KINZOKU K.K.), November 12, 1983. In this document, solar cells of the N-on-P type and solar cells of the P-on-N type are arranged alternately, and their adjoining back side electrodes are connected via metal connectors respectively. However, still this design of a solar cell array leaves unused space between the solar cells.
  • There therefore consists a continuing need for improving the efficiency of a solar cell array.
  • According to the invention, this object is solved, in a solar cell module as described above, as set out in claim 1,in that the first lateral side of the N-on-P first solar cell forms an acute angle at a first top surface edge, the first lateral side of the P-on-N second solar cell forms an acute angle at a first top surface edge, and the N-on-P first solar cell and the P-on-N second solar cell are positioned laterally adjacent each other such that the first top surface edges of said cells are in contact.
  • According to another aspect of the present invention, the solar cell modules are connected in the form of a solar cell array. A more efficient array is thus obtained which utilizes the benefits achievable through the use of known solar cell materials of construction. The solar cell array is also not less resistant to radiation damage in a solar space environment than existing types of arrays constructed from the same materials of construction. The present invention provides these and related advantages.
  • In accordance with a preferred embodiment of the invention, gallium arsenide solar cells are used. Arrays employing the improved solar cell module require less complex interconnection hardware and procedures, allow closer packaging of the individual solar cells to achieve increased electrical output per unit area of the array, and provide decreased problems resulting from differential thermal expansion of the individual cells in the array. The solar cell arrays of the invention can otherwise be used in a fashion identical with that of existing solar cell arrays, and have the same resistance to radiation damage.
  • In accordance with a preferred embodiment of the invention, a solar cell module comprises an N-on-P solar cell laterally joined to a P-on-N solar cell, and a conventional array of connector grids that now extend across the top surfaces of both cells. A solar cell array is formed by placing such modules laterally adjacent to each other and electrically connecting adjacent bottom surfaces of the p-layer of the N-on-P solar cell to the n-layer of the adjacent P-on-N solar cell of the adjacent module. When the adjacent modules are connected in this fashion, no top bus bar connections are required, so that there is no shading of a large portion of each solar cell module, with consequent reduced efficiency, due to top bus bar connections. Since the bus bar connections typically shade a much larger portion of the solar cell than the fine grids, an appreciable increase in the active current generating area is realized.
  • In yet another embodiment of the invention, each cell of the solar cell module has a separate connector grid on its top surface. A corresponding connector grid is applied to the bottom surface of the transparent cover which extends across the pair of cells in a module, thus connecting the top layers of adjacent cells. A solar cell array is formed by placing such modules laterally adjacent each other and electrically connecting adjacent bottom surfaces of the p-layer of the N-on-P solar cell to the n-layer of the adjacent P-on-N solar cell of the adjacent module.
  • The use of laterally adjacent, geometrically alternating N-on-P and P-on-N solar cells in a solar cell array allows increased ease of construction of the solar cell array, since laterally adjacent n-type and p-type layers can be connected directly together, without the need for top-to-bottom connectors such as "z" type connectors. Consequently, the solar cells may be more tightly packed in the solar cell array, leading to higher array efficiencies. Further, modules may be constructed to be joined in an array which has no top bus bar connections that shade a large portion of the active area of the array. Other features and advantages of the present invention will become apparent from the dependent claims and the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by the way of example, the principles of the invention.
    In the drawings,
    • Fig. 1 is an elevational view of a conventional P-on-N solar cell;
    • Fig. 2 is an elevational view of a conventional N-on-P solar cell;
    • Fig. 3 is an elevational view of a conventional solar cell array incorporating P-on-N solar cells;
    • Fig. 4 is a top plan view of the solar cell array of Fig. 3;
    • Fig. 5 is an elevational view of a solar cell module according to the present invention utilizing alternating P-on-N and N-on-P solar cells;
    • Fig. 6 is a top plan view of the solar cell array of Fig. 5; and
    • Fig. 7 is an elevational view of a solar cell module utilizing a connector grid on a cover glass to electrically interconnect the top surfaces of adjacent solar cells.
  • A conventional P-on-N gallium arsenide solar cell 10, as illustrated in Fig. 1, is prepared in the following manner. The solar cell 10 is fabricated on a gallium arsenide single crystal substrate 12, which may be prepared by any of several well established techniques. Most commonly, a gallium arsenide single crystal is fabricated by the horizontal Bridgeman technique. Substrates suitable for use in the preparation of solar cells are prepared by slicing wafers about 200 micrometers thick from the solidified single crystal. The surface orientation of the wafers is typically selected to be about (100) (cubic Miller indices notation). Gross damage induced during the slicing procedure is removed by polishing the wafer on successively finer grits of metallographic polishing paper, finishing with a 4/0 diamond paste. The polished wafer is then etched in a solution of hydrogen peroxide and ammonium hydroxide to remove any residual polishing damage.
  • A single crystal layer 14 of n-type gallium arsenide is epitaxially deposited overlying the gallium arsenide single crystal substrate 12. The n-type gallium arsenide of the layer 14 preferably has a net charge carrier concentration of about 10¹⁸ per cubic centimeter and a thickness of about 10 micrometers.
  • A single crystal layer 16 of p-type gallium arsenide is next epitaxially deposited overlying the layer 14 of n-type gallium arsenide. Preferably, the p-type gallium arsenide in the layer 16 has a net charge carrier concentration of about 10¹⁸ per cubic centimeter, with a thickness of about 0.5 micrometers or less. The junction between the layer 14 of n-type gallium arsenide and the layer 16 of p-type gallium arsenide provides a basic solar cell, but the operation of this solar cell is adversely affected by surface charge recombination at the top surface of the layer 16, unless charge recombination is inhibited. Conventionally, to inhibit surface charge recombination, a p+ gallium aluminum arsenide single crystal inhibitory layer 18 is epitaxially deposited on top of the layer 16 of p-type gallium arsenide. The p+ gallium aluminum arsenide layer 18 preferably has a net charge carrier concentration of about 2 x 10¹⁸ per cubic centimeter, with a thickness of about 0.1 micrometers. A typical composition of gallium aluminum arsenide having these characteristics is about Ga0.7Al0.3As.
  • The layers 14, 16 and 18 are deposited by techniques well known in the art, preferably liquid phase epitaxial growth or vapor phase metal-organic chemical vapor deposition. The vapor phase procedure is described above. Vapor phase metal-organic chemical vapor deposition takes place when tri-metal gallium in a gaseous form mixes with arsine gas. The mixture decomposes into gallium arsenide and is deposited on a gallium arsenide substrate at 750°C in a low-pressure chamber. The liquid phase epitaxial growth of gallium arsenide solar cells is accomplished by dipping substrates of gallium arsenide into a gallium melt saturated with gallium arsenide. This process is slightly different than the vapor phase method. It is performed with the melt at 750°C in a sealed, nitrogen purged system. The net charge carriers are diffused subsequently into the layers.
  • To lower the electrical resistance and to facilitate electrical connection to the upper surfaces of the solar cell 10, a metallic connector grid 20 is deposited on an upper face 22 of the solar cell 10. The metal is deposited in a vacuum environment using conventional sputtering or vapor deposition techniques. The individual very thin lines of the connector grid 20 are spaced about two millimeters apart, so that electron charge carriers may readily diffuse through the semiconductor layers 14, 16 and 18 to be collected by the individual elements of the connector grid 20. If the individual elements are too widely spaced, they cannot readily collect the electrons and a loss of voltage will occur.
  • A transparent cover 24 is attached to the upper face 22. The composition and thickness of the transparent cover 24 are selected to optimize the electrical performance of the solar cell 10. Preferably, the transparent cover 24 is a silica glass such as Corning Glass type 7940, having a thickness of about 200 micrometers. The transparent cover 24 performs three important functions. First, the cover 24 allows light to pass through to the layers 14 and 16. Second, the cover 24 supports the remaining elements of the solar cell 10. Third, the cover 24 protects the remaining elements of the solar cell 10 from physical damage and certain types of radiation in a space environment such as low energy protons and ultra violet light.
  • The transparent cover 24 may be bonded to the layer 18 by any suitable technique, such as by a transparent adhesive or electrostatic bonding. It is preferable that the bonding technique permit retention of the bond at temperatures as high as about 200°C, to resist delamination in use if thermal annealing is employed to reduce radiation degradation. High temperature adhesives of high molecular weight compounds such as carborane siloxane polymer have been found to be operable.
  • As illustrated in FIG. 2, a conventional N-on-P gallium arsenide solar cell 26 is prepared by furnishing a gallium arsenide single crystal substrate 28 substantially identical to the substrate 12 previously described. A single crystal layer 30 of p+ gallium aluminum arsenide is epitaxially deposited overlying the substrate 28, to inhibit surface charge recombination. A single crystal layer 32 of p-type gallium arsenide is then epitaxially deposited overlying the layer 30. An n-type gallium arsenide layer 34 is then epitaxially deposited over the layer 32. A connector grid 36 without the bus bar is deposited upon an upper face of the layer 34 of n-type gallium arsenide. Finally, a transparent cover 40 is fastened over the connector grid 36 and the layer 34.
  • The characteristics of the layers 30, 32 and 34, the methods for depositing the layers 30, 32 and 34, the geometrical arrangement, structure and method of depositing the connector grid 36, and the structure and method of attaching the transparent cover 40 in relation to the N-on-P gallium arsenide solar cell 26 are all substantially identical to the corresponding aspects of the P-on-N gallium arsenide solar cell 10, described in the preceding paragraphs. Only the order of depositing the active layers 30, 32 and 34 to form the N-on-P solar cell 26 differs from the order of depositing the layers 14, 16 and 18 to form the P-on-N solar cell 10 is different.
  • It has been found that the N-on-P solar cell 26 exhibits nearly identical electrical performance and resistance to radiation damage as the P-on-N solar cell 10. In fact, the electrical performance of the N-on-P gallium arsenide solar cell degrades slightly less with the passage of time, as compared with a P-on-N gallium arsenide solar cell. The maximum power available from the P-on-N solar cell will degrade approximately 20 percent when exposed to 1 MEV electrons at a fluence of 10¹⁵, which is equivalent to almost 5 years in synchronous orbit.
  • Individual P-on-N solar cells 10 each produce a voltage output of about 0.9 volts, which is too low a voltage for any practical application in a space environment. The P-on-N solar cells 10 are therefore conventionally hooked together in a series fashion to obtain an output voltage equal to the sum of the voltages produced by the individual solar cells 10. Identical groups of the solar cells joined in series are then hooked together in a parallel fashion to achieve increased electrical currents as required.
  • FIGS. 3 and 4 illustrate the manner of interconnecting conventional P-on-N solar cells to form a conventional solar cell array 42. To achieve a series connection, the top or p-type layer 16 of one solar cell 10 must be electrically connected through the P+ layer 18 to the bottom or n-type layer 14 through the substrate 12 of the adjacent cell. The type of connectors utilized are termed "z-connectors" 44, because of their shape when viewed in an elevational view. The z-connectors 44 are joined to the bus bars that interconnect the grid 20 on each cell in order to connect these elements to the adjacent solar cell 10. The conventional z-connector 44 includes a horizontal portion at each end and an inclined portion extending from the top to bottom of the solar cells. The horizontal portions are soldered or otherwise connected to the bus bars of the solar cell 10 to form the connections. The area of the attachment under the horizontal portion of the z-connector 44 and the bus bar is inactive and cannot produce an electrical current, since the junction between the layers 14 and 16 is shaded from the rays of the sun by the connector and bus bar. The electrical output of a conventional solar cell array 42 is therefore reduced below its potential current output due to the spacing between adjacent solar cells, which must be maintained to accommodate the z-connector 44, and the inactive area shaded by the connector and bus bar extending along one side of each solar cell.
  • FIGS. 5 and 6 illustrate a first configuration 48 of the solar cell module of the present invention wherein a P-on-N solar cell 10 and an N-on-P solar cell 26 are grouped together as a module 56. In such a module 56, a connector grid 58 extends continuously across the upper surface of the module 56 between the solar cells 10 and 26, electrically connecting the p layer of the P-on-N solar cell 10 to the n layer of the N-on-P solar cell 26. A non-conductive adhesive 50 is used to tightly bond the cells 10 and 26 together to form each module 56. This allows the connector grid 58 to be vapor deposited so as to extend across the top surfaces of the cells. As seen exaggerated in FIG. 5, each cell is formed at a very slight angle from the normal crystal so that when formed, the sides have a slight slope. The cells 10, 26 of each module 56 are in contact at a top surface edge 52. The angle formed by the top surface and side of each cell 10, 26 at the top surface edge 52 may typically deviate from 90° by about 1°. This provides sufficient separation of adjacent cell sides to prevent shorting of the cells while providing good electrical contact at the top surfaces and minimizes any inactive surface area. To form a solar cell array, adjacent modules 56 are connected together only at their lower surfaces, by a metallic connector 60. The metallic connector 60 provides an electrical connection from the N-on-P solar cell 26 of a first active pair 56 to the P-on-N solar cell 10 of a second active pair 56, and so on.
  • The configuration 48 is used to optimize the output efficiency of an array by reducing both geometrical components of electrical output loss found in conventional solar cell arrays 42. The loss due to the spacing between adjacent cells is drastically reduced, inasmuch as there is no spacing between the two solar cells comprising each module 56. Additionally, the need for bus bars at the upper surfaces of the solar cells is eliminated through the use of the continuous connector grid 58. That is, there is no area of the upper surface of any of the solar cells making up the configuration 48 that is inactive as a result of being shaded from the sun by an upper bus bar connecting adjacent solar cells. It is estimated that the reduction in the cell spacing can result in an increased efficiency of about 4 percent. It is further estimated the elimination of the top bus bars in the configuration 48 can result in an increased efficiency of about 6 percent. Thus, the overall improvement in efficiency, in watts per unit area of array, of the configuration 48 illustrated in FIGS. 5 and 6 can be as much as 10 percent.
  • In a second configuration shown in FIG. 7, the electrical interconnection of the solar cells 10, 26 of module 56 is provided by a conductor grid 62 on a transparent cover glass 64. Solar cell 10 includes the connector grid 20 and solar cell 26 includes the connector grid 36 as shown in Figs. 1 and 2. A grid 62 is placed on the cover glass 64 to match the grids 20 and 36 and then the cover glass grid 62 and two solar cell grids 20 and 36 are fused together to form two cell module 56. In this manner, the two cells are held rigidly together and are electrically connected. Individual modules may then be interconnected by metallic conductors along the bottom surfaces.

Claims (8)

  1. Solar cell module (56) comprising
    (1.1) an N-on-P first solar cell (26) including an n-type semiconductor layer and a p-type semiconductor layer, said first N-on-P solar cell (26) having a lateral cross-sectional configuration with a top surface and a first lateral side;
    (1.2) a P-on-N second solar cell (10) including a p-type semiconductor layer and a n-type semiconductor layer, said P-on-N second solar cell (10) having a lateral cross-sectional configuration with a top surface and a first lateral side;
    (1.3) connecting means for electrically connecting said n-type layer of said N-on-P first solar cell (26) to said p-type layer of said P-on-N second solar cell (10);
    characterized in that
    (1.4) said first lateral side of said N-on-P first solar cell (26) forms an acute angle at a first top surface edge (52),
    (1.5) said first lateral side of said P-on-N second solar cell (10) forms an acute angle at a first top surface edge (52),
    (1.6) said N-on-P first solar cell (26) and said P-on-N second solar cell (10) are positioned laterally adjacent each other such that said first top surface edges (52) of said cells (26,10) are in contact.
  2. Solar cell module (56) according to claim 1, characterized in that both said N-on-P first solar cell (26) and said P-on-N second solar cell (10) have lateral cross-sectional configurations of a parallelogram with the top surfaces and one of the lateral sides forming an acute angle at the top surface, respectively.
  3. Solar cell module (56) according to claim 1 or 2, characterized in that said connecting means comprises a grid (58) of electrical conductors extending between said n-type layer of said N-on-P first solar cell (26) and said p-type layer of said P-on-N second solar cell (10).
  4. Solar cell module (56) according to any of the preceding claims, characterized by a transparent cover (64) over said top surfaces and said connecting means.
  5. Solar cell module (56) according to claim 4, characterized in that said connecting means comprises:
    (5.1) a first grid (36) of electrical conductors on said n-type layer of said N-on-P first solar cell (26);
    (5.2) a second grid (20) of electrical conductors on said p-type layer of said P-on-N second solar cell (10);
    (5.3) a corresponding grid (62) of electrical conductors on the bottom surface of said transparent cover (64) such that said first grid (36) is electrically connected to said second grid (20).
  6. Solar cell module (56) according to any of the preceding claims, characterized in that said N-on-P first solar cell (26) and said P-on-N second solar cell (10) are gallium arsenide solar cells.
  7. Solar cell array (48) comprising a plurality of solar cell modules, (56) according to any of claims 2 to 6, characterized by means (60) for electrically interconnecting the bottom surfaces of such adjacent P-on-N second solar cells (10) and N-on-P first solar cells (26) of said solar cell modules (56) which are not in contact at their top surface edges.
  8. Solar cell array (48) according to claim 7, characterized in that said means (60) for electrically interconnecting adjacent solar cells includes a plurality of metallic conductors.
EP87907641A 1985-09-09 1987-10-15 Solar cell system Expired - Lifetime EP0288543B1 (en)

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US929571 1986-11-12
US06/929,571 US4753683A (en) 1985-09-09 1986-11-12 Gallium arsenide solar cell system

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EP0288543A1 EP0288543A1 (en) 1988-11-02
EP0288543B1 true EP0288543B1 (en) 1992-11-19

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JP (1) JPH0656897B2 (en)
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WO (1) WO1988003706A1 (en)

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CA1277754C (en) 1990-12-11
US4753683A (en) 1988-06-28
DE3782733T2 (en) 1993-06-09
DE3782733D1 (en) 1992-12-24
EP0288543A1 (en) 1988-11-02
JPH01501433A (en) 1989-05-18
JPH0656897B2 (en) 1994-07-27
WO1988003706A1 (en) 1988-05-19

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